Javier Cortejoso said “I think the key word that should be in the answer to be considered correct is “myelomeningocele”. I'm going to explain it.

Spinal dysraphisms include all congenital spinal disorders in which there is anomalous differentiation and/or incomplete closure of dorsal midline structures: skin, muscles, vertebrae, meninges, and nervous tissue. The term “spina bifida” refers to defective fusion of posterior spinal bony elements although is widely used to refer to spinal dysraphisms in general.

Spinal dysraphisms are classically categorized in two major subsets: open spinal dysraphisms (OSD, characterized by exposure of the nervous tissue to the environment) and closed spinal dysraphisms (CSD, no exposed neural tissue, being covered by skin). CSDs are more numerous than OSDs, accounting for approximately two thirds of patients. Four varieties of OSD exist (myelomeningocele, myelocele, hemimyelomeningocele, and hemimyelocele), with myelomeningocele encompassing 98.8% of cases. Usually, are located at the lumbar or lumbosacral level and are diagnosed antenatally by ultrasound. CSDs are much more heterogeneous (meningocele, lipomyelocele, lipomyelomeningocele, or terminal myelocystocele) than OSDs, and some of them are not clinically evident at birth.

Prenatal detection of OSDs by fetal ultrasound was greatly improved in the mid-1980s by the description of a number of characteristic cranial findings which were found to be more easily appreciated than directly visualizing the spinal defect. In OSDs there is displacement of the medulla, fourth ventricle, and cerebellum through the foramen magnum, causing what is known as Chiari type II malformation. During prenatal ultrasonography, characteristic malformations include the lemon sign, the banana sign, and obliteration of the cisterna magna, usually accompanied by ventriculomegaly.

Although macroscopically similar to a myeolomeningocele, meningocele is a closed spina bifida, whereby the defect consists of herniation exclusively of the meninges through the vertebral column. By ultrasound the characteristics of the cystic mass are comparable with that of the myelomeningocele, although they lack septa in the herniated mass, and the cranial anatomy is unremarkable, without the typical findings of type II Chiari malformation.
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